Post-transplant lymphoproliferative disease (PTLD) is a morphologically complex disorder that ranges from benign B cell hyperplasia to malignant lymphoma. Epstein-Barr virus (EBV) B cell lymphomas are the hallmark of PTLD and are associated with significant morbidity and mortality. During the previous funding period we identified specific signaling pathways that confer a survival advantage to EBV-infected B cells despite significant frequencies of EBV-specific CD8+ T cells in the circulation of transplant recipients. We also established that the immunosuppressive sirolimus (RAPA) can directly inhibit the growth of EBV-infected B cells. The objective of this research is to defme the immune alterations that contribute to the autonomous growth of EBV-associated B cell lymphomas. To accomplish this objective we propose four Specific Aims. In Specific Aim 1 we will determine the requirement for IL- 10 and its associated Jak/STAT signal transduction pathway in sustaining the growth of EBV-infected B cells. Dominant negative (DN) forms of the 1L-lO receptor (IL-1OR), STAT1 and STAT3 will be transduced into EBV-infected B cells using a lentivirus-based retroviral transduction system to evaluate the effect on cell growth. A SCID mouse model of EBV+ B cell lymphoma will be used to test the effect of blockade of IL-lO on tumor growth. Specific Aim 2 will examine the mechanism by which EBV-infected B cells are resistant to death receptor-induced apoptosis. The proximal events in the Fas and TRAIL-DR4/DR5 cell death pathways will be characterized by two-dimensional gel electrophoresis and DNA microarray. The role of the decoy receptors DcR1 and DcR2 in resistance to TRAIL cytotoxicity will be examined. The contribution of the EBV latent genes LMP1 and EBNA2 to resistance to apoptosis will also be determined. In Specific Aim 3 MHC/peptide tetramers containing immunodominant epitopes of EBV antigens will be used to identify EBV-specific CD8+ T cells in transplant recipients and the functional properties of these T cells will then be assessed. The effects of immunosuppression on the generation of functional EBV-specific CD8+ T cells will be determined in the SCID/EBV B cell lymphoma model. Aim 4 will determine the mechanism by which RAPA inhibits growth of EBV-infected B cells with specific focus on apoptosis, cell cycle proteins and the JakISTAT pathway. Elucidation of the immune mechanisms involved in PTLD will provide novel opportunities for treatment of this serious disease.